title: Spin fluctuations and pairing symmetry in AxFe₂-ySe₂: dual effect of the itinerant and the localized nature of electrons.
abstract: We investigate the spin fluctuations and the pairing symmetry in AxFe2-ySe2 by the fluctuation exchange approximation. Besides the on-site interactions, the next-nearest-neighbor antiferromagnetic coupling J2 is also included. We find that both the itinerant and the localized natures of electrons are important to describe recent experimental results on the spin fluctuations and the pairing symmetry. In particular, a small J2 coupling can change the pairing gap from the d-wave symmetry to the extended s-wave symmetry. We have also studied the real-space structures of the gap functions for different orbits in order to gain more insight into the nature of the pairing mechanism.
authors.affiliation: National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, People's Republic of China.
authors.forename: Shun-Li
authors.initials: SL
authors.lastname: Yu
authors.forename: Jia
authors.initials: J
authors.lastname: Guo
authors.forename: Jian-Xin
authors.initials: JX
authors.lastname: Li